1. Field of the Invention
The present invention relates to non-aqueous electrolyte secondary batteries, and more particularly, to non-aqueous electrolyte secondary batteries excellent in cycle characteristics and charge storage characteristics.
2. Background Art
Mobile information terminals such as portable telephones and notebook personal computers are increasingly sophisticated and increasingly reduced in size and weight these days. These terminals use as mobile power supplies a variety of non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries having a high-energy density and a high capacity.
In recent years, these batteries are expected to have a higher capacity to meet the demand for higher sophistication of these devices.
One technique known to increase battery capacity is to improve the use efficiency of a positive electrode active material by charging a positive electrode until the potential of the positive electrode active material exceeds 4.3V versus lithium.
However, charging to high voltages accelerates undesirable reactions such as oxidative decomposition of an electrolyte on the positive electrode side, thereby causing degradation in cycle characteristics. Moreover, if a battery in a charged state is stored at high temperatures, there may be a decrease in discharge capacity after storage or an increase in the thickness of the battery due to gas generated by the reaction between the positive electrode and an electrolytic solution.
To improve the cycle characteristics and charge storage characteristics of non-aqueous electrolyte secondary batteries, it has been proposed to add a sulfonic acid ester compound to a non-aqueous electrolytic solution.
For example, Patent Document 1 shows a technique in which a sulfonic acid ester compound is added to an electrolyte so as to increase the open circuit voltage between battery terminals after charging to high voltages.
Patent Document 2 shows a technique in which a sulfonic acid ester compound such as 1,4-butanediol dimethanesulfonate is added to an electrolyte so as to produce a battery having a large charge-discharge capacity and little degradation during high-temperature storage in a charged state.
Patent Documents 3 to 6 each show a technique in which a sulfonic acid ester compound is added to an electrolytic solution so as to improve cycle characteristics and other features of non-aqueous electrolyte secondary batteries.
Patent Documents 7 and 8 each show a technique in which a 1,3-dioxane-based solvent is used to improve the charge-discharge characteristics of a non-aqueous electrolyte.
Patent Document 1: Japanese Patent Unexamined Publication No. 2006-351337
Patent Document 2: Japanese Patent Unexamined Publication No. 2005-285630
Patent Document 3: WO2003/077351
Patent Document 4: WO2005/029631
Patent Document 5: Japanese Patent Unexamined Publication No. 2000-195545
Patent Document 6: Japanese Patent Unexamined Publication No. 2001-313071
Patent Document 7: Japanese Patent Unexamined Publication No. S63-152886
Patent Document 8: Japanese Patent Unexamined Publication No. 2000-40524